1. Field of the Invention
The present invention relates generally to a Hybrid Electric Vehicle (HEV), and specifically a method and system for an HEV to determine when the engine should operate during vehicle idle and under what parameters.
2. Discussion of the Prior Art
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles powered by Internal Combustion Engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Unfortunately, electric vehicles have limited range and power capabilities. Further, electric vehicles need substantial time to recharge their batteries. An alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles are typically called Hybrid Electric Vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 (Severinsky).
The HEV is described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a Series Hybrid Electric Vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A Parallel Hybrid Electrical Vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that together provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A Parallel/Series Hybrid Electric Vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is typically known as a xe2x80x9cpowersplitxe2x80x9d configuration. In the PSHEV, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque powers the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery if a regenerative braking system is used. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, generator motor and traction motor can provide a continuous variable transmission (CVT) effect. Further, the HEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.
The desirability of combining an ICE with electric motors is clear. There is great potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or drive-ability. Nevertheless, new ways must be developed to optimize the HEV""s potential benefits.
One such area of development is HEV engine operation. In an HEV, the engine has multiple functions. The engine""s first and most obvious purpose is to provide wheel torque. The engine also is necessary for many secondary functions. While the engine is running the HEV can also: spin the generator to charge a battery, purge a fuel vapor canister, mature its adaptive fuel tables, operate its air-conditioning (A/C) system, replenish vacuum to the A/C and brake systems, and maintain optimal engine and catalyst temperatures. Each of these secondary functions has separate optimal engine operating conditions and no one idle speed is optimal for each. Therefore, if the engine is operating at optimal speed for one secondary function, while other functions are possible, they may not be completed as efficiently or quickly.
The HEV engine has many functions that require it to be running. Nevertheless, the main goals of HEVs are reduction of fuel usage, emissions, and increasing run time (i.e., the length of time the vehicle can operate without refueling or recharging). The HEV can achieve these goals by turning the engine off when it is not needed. Fortunately, the secondary HEV engine functions do not require the engine to run all the time. The battery and traction motor are capable of providing sufficient driving torque for many driving conditions.
Engine usage parameters, and specifically, engine run time, are divided into two categories including drive conditions, where wheel torque is supplied, and idle conditions. Idle conditions exist when the vehicle is not moving. Generally, it is desirable to turn the engine off during idle conditions. Nevertheless, the secondary functions may still require a running engine. The prior art has not addressed the problem of determining when the engine should run during idle conditions and what parameters optimize the performance of the desired secondary function.
Accordingly, an object of the present invention is to provide a method and system to determine when the engine should operate during vehicle idle and under what parameters for a hybrid electric vehicle (HEV). The present invention provides a method and system to implement a logic arbitration scheme allowing a Vehicle System Controller (VSC) to determine if the engine should run during idle conditions and, if so, at what operating parameters.
The method and system to determine engine operation during idle comprises determining if idle conditions are met, determining if engine operation is necessary, determining a method of engine control, and operating the engine at the most efficient operating parameters. Vehicle speed establishes whether idle conditions exist or whether the vehicle is in motion. Accelerator position is established to determine torque requests. The method and system also determine when engine operation is necessary. A controller determines whether the battery needs charging, whether vacuum needs replenishing in the climate control system or brake system reservoir, whether a vapor canister requires purging, whether the Adaptive Fuel Tables require fast adapting, whether the engine or catalyst temperatures are unacceptably low, and if air conditioning has been requested. If any determinations are positive, the controller turns (sets to 1) the appropriate xe2x80x9cengine onxe2x80x9d idle flag for that function and proceeds to determine the appropriate engine control mode.
To determine the appropriate method of engine control, the controller determines whether the battery state of charge is too high or whether generator failure exists. If the state of charge is not too high and generator failure does not exist, the engine is run in torque control mode through a generator controller. Otherwise, the engine is run in speed control mode through powertrain controllers. If the engine is operated in speed control mode, typical engine control is employed through the use of spark and air feedback. However, if torque control mode is employed, the vehicle is run at optimum conditions by the generator controller for the desired function.
The system for determining whether the engine should run during idle comprises many vehicle components including an engine, a vehicle system controller, battery, battery state of charge determination system, climate control system requests, brake control system, climate system and brake system reservoir vacuum determination, a vapor canister, vapor canister purging need determination, adaptive fuel tables, adaptive fuel tables mature determination, engine and catalyst temperature determination, an air conditioning system, a generator, a means to control HEV components including a generator controller, a powertrain controller and a battery controller.